/Engine/Source/Runtime/Engine/Classes/Kismet/GameplayStatics.h
Sets what platform user id a player should be using. This only works for local player controllers.
static void SetPlayerPlatformUserId ( [APlayerController](API\Runtime\Engine\GameFramework\APlayerController) * PlayerController, [FPlatformUserId](API\Runtime\Core\Misc\FPlatformUserId) UserId )